Flat multiconductor ribbon cable is used extensively in the electronics industry, especially in the computer field. Cable of this type typically includes a plurality of electrical conductors arranged in side-by-side spaced orientation. These conductors are surrounded by an insulative casing which electrically isolates each of the conductors.
Several factors affect the quality and reliability of these cables. The size of each conductor, measured by the cross-sectional area, dictates the amount of signal current that each conductor can carry. The amount of signal current carried is directly proportional to the size of the conductor.
In addition, the impedance value of the cable is related, in part, to the spacing between adjacent conductors. In cables having similar dielectric constants, the greater the space between adjacent conductors (i.e. the more insulating mass therebetween) the greater the impedance value of the cable.
It is desirable to construct a cable which is capable of carrying high signal currents while also having a high impedance value. Thus, cable having large conductors and ample spacing between adjacent conductors would be ideal. However, in the modern computer environment, a cable assembly of this construction is not practical. In fact, the current state of the computer industry is to require smaller cable, i.e. cable with conductors spaced at a smaller pitch, while maintaining the high signal carrying capabilities of the cable as well as the high impedance value. However, when spacing conductors at a smaller pitch, the insulating mass between facing surfaces of adjacent conductors is reduced. This results in lowering the impedance value of the cable. Side-by-side round conductors, typically used in cables of this type, when spaced at a small pitch, would result in the facing curved surfaces of adjacent conductors being in close proximity. This would cause the impedance value to be lowered beyond tolerability.
The art has seen the use of rectangular conductors in flat multiconductor cable assemblies which permit the conductors to be placed on a smaller pitch while maintaining more insulating mass between facing surfaces of adjacent conductors. However, rectangular conductors are difficult to form and are more expensive than conventional round conductors. Further, in most computer applications, mass cable termination to insulation displacing contacts of electrical connectors is desired. Rectangular conductors are inherently difficult to mass terminate in this manner.
It is therefore desirable to provide a flat multiconductor electrical cable which permits spacing of electrical conductors at a reduced pitch while maintaining a high degree of signal transmission and a high impedance value.